Ultrastructural morphology of the uredium and collar formation during urediosporogenesis of Uromyces transversalis on gladiolus

Abstract

The transverse uredia of Uromyces transversalis on gladiolus leaves were investigated by scanning and transmission electron microscopy. The basal cell forms one or more protuberances distally, each being delimited by a septum to become a urediospore initial. The initial elongates and lays down a septum to form a urediospore and pedicel. The first protuberance on the basal cell forms holoblastically, and evidence is found at the same locus for the subsequent enteroblastic formation of up to three successive urediospore initials. The pedicel wall of a spore thus formed remains on the basal cell and becomes a collar around the next protuberance. The basal layer of the two-layered septum that delimited the pedicel from the basal cell grows out to form the wall of the subsequent protuberance, and in the process ruptures and laterally displaces the terminal septal layer. A new basipetal septum forms to delimit the subsequent urediospore initial. In this manner, several collars form retrogressively and concentrically at one locus.